It has become increasingly desirable in our communications-oriented society to upgrade and improve business and residential telephone equipment by adding telephones having improved functionality and increasing the number of incoming telephone lines at minimal cost. However, since one cannot expect to find more than a single wire-pair at any given location, it is frequently necessary to supply additional wiring beyond the single wire-pair used for basic telephone service in order to increase the number of communication channels. Costs associated with adding or relocating wires can be significant. Furthermore, many commercially available systems that are used to increase information distribution capacity are incompatible with existing telephone equipment, so a user's investment is immediately eroded.
From a convenience standpoint, it is desirable for a customer to merely purchase a telephone product, take it home, and plug it into an existing telephone jack. Many systems that utilize the local telephone wire-pair at a user's premises require that a master station be placed in a series connection with the incoming wire-pair from the telephone central office. Series connections require that internal wiring be modified which usually means that a telephone installer or an electrician needs to be hired.
A problem, however, with having multiple telephone stations share the same wire-pair is that each one presents a parallel 600 ohm AC impedance in its off-hook state. As a result, both the transmit and receive signal levels are reduced so that users frequently strain to hear each other when more than two are involved in the conversation.
It is therefore an object of the present invention to provide telephone apparatus having improved functionality and is compatible with existing telephone extensions that share a common wire-pair.
It is another object of the invention to provide substantially constant transmit and receive signal levels, regardless of the number of stations at one premises, in a multiple party conferencing call.